U.S. Pat. No. 7,225,308 to Melament, et al discloses an inexpensive storage system and methods of managing such a system. In one preferred embodiment, the system includes a high performance high reliability storage medium configured for initial storage of data, a low performance high reliability storage medium configured for backup of data initially stored on the high performance high reliability storage medium, and a high performance low reliability storage medium, configured to receive data transferred from the high performance high reliability storage medium, after the data has been backed up on the low performance high reliability storage medium. This significantly reduces the cost of the system without substantially comprising performance. Reliability is likewise maintained owing to the high reliability backup.
U.S. Pat. No. 5,392,244 to Jacobson, et al. discloses a storage system which comprises a disk array having a plurality of disks, a disk array controller for coordinating data transfer to and from the disks, and a RAID management system for mapping two different RAID areas onto the disks. The RAID management system stores data in one of the RAID areas according to mirror redundancy, and stores data in the other RAID area according to parity redundancy. The RAID management system then shifts or migrates data between the mirror and parity RAID areas on the disks in accordance with a predefined performance protocol, such as data access recency or access frequency.
US Patent Application Publication No. 20080154993 to Unmesh et al. discloses a multiple QoS file system and methods of processing files at different QoS according to rules. The invention allocates multiple VLUNs at different qualities of service to the multiQoS file system. Using the rules, the file system chooses an initial QoS for a file when created. Thereafter, the file system moves files to different QoS using rules. Users of the file system see a single unified space of files, while administrators place files on storage with the new cost and performance according to attributes of the files. A multiQoS file system enhances the descriptive information for each file to contain the chosen QoS for the file.
US Patent Application Publication No. 20010018728 to Topham et al. discloses a RAID-device with a pair of non-volatile solid state data storage devices and one or more rotating disk drives, giving improved access time performance to the array. Data is staged on the pair of solid state data storage devices, and periodically backed up to the rotating disk drive(s). Topham et al. suggests using Dynamic Random Access Memory (DRAM) arrays as an alternative to the solid state data storage devices. DRAM devices are intrinsically volatile, and lose their stored data when power is removed. In order to make a non-volatile solid state data storage device, Topham et al. suggest a combination of an array of DRAM devices, and a battery power supply in a casing. Topham et al. asserts that although DRAMs provide better performance in terms of read and write access times than a comparable MRAM unit, there is the disadvantage of the need to provide a battery back-up to overcome the intrinsic volatility of DRAM devices to provide a non-volatile DRAM data storage unit.